Andy Roddick believes Roger Federer will be a tough man to beat in Sunday's Australian Open final.

That is if he serves as well as he did during their semi-final match on Thursday evening.

The world number two reached his 18th grand slam final with a 6-2 7-5 7-5 win against Roddick and will face either Rafael Nadal or Fernando Verdasco, who play their semi-final on Friday.

But of more surprise was the fact he sent down double the number of aces (16) as the big serving American seventh seed, had 66% of first serves in and won 83% of the points on his first serve.

"For some reason he seems to serve pretty well against me. I think it was up around maybe 70% first serves, which is just high for him. He's not really up in that area a lot. So when he does that, it makes it pretty tough," Roddick said.

"I think if Roger serves the way he did tonight it's going to be real tough for anybody to beat him.

"If it's down in the 55 where someone is getting looks at second serves, who knows?"

Federer himself was pleased his serve had been able to get him out of potentially tricky moments in the match, which was played with the Rod Laver Arena roof open following a drop in temperature to the low 30 degrees Celsius after highs earlier in the day of around 44 degrees.

"I served well when I had to," the three-time Australian Open champion said.

"So many times at 30-all I came up with big aces and that saved me from a lot of trouble which was good because Andy was returning well and playing aggressively."

Federer broke the Roddick serve twice on the way to winning the first set and felt that had set the tone for the match, even though the American responded well to push him harder in the remaining sets.

"I had a couple good games where I served really well in the first set, and that gave me a lot of confidence going into the second one," said the Swiss star who is hoping to equal Pete Sampras' record of 14 grand slam titles on Sunday.

"I was moving well and getting a lot of balls back and making it difficult for Andy to get the upper hand from the baseline."

A hustling Roddick tried everything from drop shots to bullet-like serves to find a way through the Federer armoury.

By and large though the second seed had an answer for everything the American, who hit 38 winners compared to Federer's 51, could send his way.

And Roddick conceded: "The thing about Roger is you can know where to go, and you can still come out on the bad end of it sometimes.

"So that's where it differs from a lot of people. A lot of people, you know exactly what you have to do and the majority of the time you execute it, you're going to come out on the good end it of.

"That part is a little bit frustrating at times.

"Overall, it was an okay match. He just beat me. It's plain and simple.

"I hit the ball pretty well. Both of us had pretty good stats he just came up with shots when he needed to.

"That's what he does."

Roddick has only ever beaten Federer in two of their previous 17 meetings - the most recent success coming in Miami last year.

But he never looked like repeating that in Rod Laver Arena tonight.

The second seed took the lead for the first time in the third game of the opening set and after Roddick had squandered a break point opportunity he was made to pay dearly for that in the fifth when Federer broke him again then comfortably held serve for a 5-1 lead.

Federer found the net a couple of times in the next game to help Roddick hold his serve, although the American was clearly disgruntled by a line call and subsequent challenge and made his frustrations known to the chair umpire Enric Molina at the change of ends.

Federer however calmly served out for the set. The second set was far closer with break point chances few and far between.

But just when it appeared to be heading for a tie break Roddick got broken in the 11th game when Federer hit a blistering winner down the line after looking seemingly out of the point, before the American found the net again.

Federer then held his serve to love to wrap up the second set.

The third set followed a similar pattern.

After being given a code violation for swearing Roddick produced an audacious sliced backhand to help him on his way to holding his serve.

But the break eventually came in the 11th game and Federer served for the match which he sealed with a down the line winner.